1. Field of the Invention
This invention relates to the mixing of liquids in controlled proportions, and more particularly to the mixing of liquid components in pre-selected proportions to provide a solvent for use in liquid chromatography.
2. Description of the Prior Art
Many operations require the use of various mixtures of two or more liquid components, and need exists for a device capable of mixing a plurality of liquid components in pre-selected proportions to form a mixture having a desired composition, and which permits ready adjustment of the selected proportions.
One particular application for such device is in the field of liquid chromatography. Chromatography is the technique of separating a mixture of chemical elements and/or compounds by passing a quantity, or slug, of the mixture to be separated in a continuous stream of mobile carrier phase, which can be a suitable gas or liquid, through an elongated bed of a solid absorbent material contained in a chromatograph column. As the chemical mixture is carried through the column by the mobile phase, the various constituents of the mixture are adsorbed and desorbed from the solid absorbent at different rates so that the various components will tend to separate in the column and exit the column at different times. This separation allows the components to be individually collected or identified by a suitable analytical procedure.
The solvents employed as the mobile carrier phase in liquid chromatography determine, in part, the rate at which the components of the mixture to be separated travel through the column. These solvents are often admixtures of two or more liquid components mixed in the proper proportions to provide a solvent of the desired composition. However, it is frequently the case that the optimum solvent composition cannot be predetermined. Consequently, it is often desirable to change the solvent composition between or during runs. Also, in gradient elution chromatography, the composition of the solvent is changed during the course of the elution. Thus, in many liquid chromatographic operations there must be provided a wide variety of multicomponent solvent mixtures containing different proportions of components. Hand mixing of the solvent compositions is laborious and time consuming.
Much effort has been expended in developing apparatus for admixing fluids in predetermined proportions. The devices disclosed in U.S. Pat. No. 3,647,002 to Lindsay and U.S. Pat. No. 3,693,653 to Cramer et al. are examples of such apparatus. Liquid proportioning devices for use in liquid chromatography are disclosed in U.S. Pat. No. 3,446,057 to Bakalyar et al.; in Introduction to Modern Liquid Chromatography by L. R. Snyder et al., Wiley-Interscience Publications, New York, N.Y., pages 110-119, (1974); and in articles by Scott, "Gradient Elution Facilities for LC Using the Continuous and Incremental Methods of Solvent Mixing", Journal of Chromatographic Science, Vol. 9, pages 385-389, (1971); by Stolyhwo et al., "Studies on the Analysis of Lipid Classes by Gradient Elution Adsorption Chromatography", Journal of Chromatographic Science, Vol. 11, pages 20-25, (1973); and by Byrne et al., "A Multifunctional Gradient Device for Use in High-Speed Liquid Chromatography", Journal of Chromatographic Science, Vol. 9, pages 592-595, October 1971. While these devices have met with varying success, need exists for a simple, low cost device capable of providing a continuous supply of a mixture of liquid components in varying pre-selected proportions.
Accordingly, a principal object of this invention is to provide an apparatus to admix a plurality of liquid components in controlled proportions to provide a solvent mixture having a desired composition.
Another object of this invention is to provide such an apparatus which is capable of readily changing the proportions of the liquid components to provide solvent mixtures of different pre-selected compositions.
A further object of the invention is to provide such an apparatus which is capable of continuously varying the proportions of said liquid components in said mixture in accordance with a predetermined program.
A still further object of this invention is to provide such an apparatus for use in conjunction with a liquid chromatograph to provide a continuous supply of solvent mixture having a predetermined composition for use as the mobile carrier phase.